After forming circuitry on a semiconductor device, it is desirable to change the state of some circuitry to provide electrical chip identification, customization of function and to substitute a spare row or column for a defective element, such as a bit. Typically, creating an electrically measured connection, termed a fuse, and attaching it to circuitry that will sense the change in state of the electrically measured connection accomplishes this. Fuses can be formed from metal lines, which are surrounded by an interlayer dielectric (ILD) and are covered by a passivation layer. When it is desired to change the state of the electrically measured connection, portions of the fuse are removed in order to create an open. Typically, a portion of the fuse is physically severed (blown) by absorbing energy from a laser, superheating, breaking the passivation layer and boiling, vaporizing or exploding. Hence, when the fuse is blown, an opening is left in the passivation layer leaving the remnant fuse and the underlying and surrounding ILD exposed.
Traditionally, aluminum is used for the metal lines of the semiconductor device. To increase the speed at which the semiconductor device operates, aluminum metal lines and interconnects are being replaced with copper. However, copper does not form a self-passivation layer like aluminum and therefore does not protect any underlying layers from corrosion as the aluminum does by the presence of the self-passivation layer. To keep the absence of the self-passivation layer from affecting the reliability of the semiconductor device, the copper fuse terminates on a refractory metal plug, which prevents corrosion resulting from the exposure to the environment of a blown fuse. The presence of the refractory metal plug prevents corrosion from spreading to other parts of the semiconductor device. In some cases, the blown copper fuse can cause delamination of the ILD and spread to adjacent parts of the semiconductor device, such as another fuse. To prevent delamination and corrosion spreading, a wet acid treatment can be used to remove the blown copper fuse, thereby exposing the refractory metal plug, which prevents corrosion. However the wet acid treatment is an additional process step that is not cost effective when compared to the failure rate of the semiconductor device due to corrosion of the blown copper fuses. Therefore, a need exits for a process for forming fuses for semiconductor devices with copper metal lines that does not add a costly process step and prevents corrosion of the fuses.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.